Abstract:

Article Preview

The polymeric precursor route based on the Pechini process was used to prepare a
mixture of nano and microcrystalline powders. The zirconia powder was stabilized with 3
mol% of yttria. Powder characteristics were evaluated by the BET technique determined the
specific area and the BJH method supplied the pore size distribution. The X-ray diffraction
results and SEM observations were carried out to characterize both the powder mixture and
the microstructures of the ceramic bodies. The sintering behavior shown in this work was
studied by dilatometric experiment, being considered the shrinkage rate and densification of
the microstructure.

Abstract: Using NH4HCO3 solution as precipitant, the ultrafine 3Y-ZrO2/Al2O3 precursors were prepared
by the liquid-phase precipitation method. The well-dispersible ZrO2/Al2O3 composite nanopowders with
particle size 10nm were obtained by calcining the precursor at 1000°C. The XRD patterns show no
γ-Al2O3 and θ-Al2O3 formed during calcination. The powders have excellent sinterability and the relative
density of specimen is up to 99% after sintering the green compacts at 1550°C. Microstructural analysis of
the sintered bodies reveals the uniform distribution of the zirconia grains in the alumina matrix.

Abstract: This work investigates the effect of nanosized Al2O3 addition on the sinterability of YSZ electrolyte. (1−x)YSZ + Al2O3 ceramics with compositions x = 0 to 0.01 were prepared by the conventional mixed oxide route from a commercial powder suspension (particle size <50 nm), and sintered at 1200 to 1500°C for 2 hours in air. Densification, phase evolution, and microstructure were characterized by SEM/EDS and XRD. An improvement in sintered density was observed for the samples with 0.2 to 0.5 mol% Al2O3, though depending on the sintering temperature. Only cubic zirconia was detected as crystalline phase, although XRD features suggested chemical interactions depending upon the amount of Al2O3. The grain size of YSZ was homogeneous and no second phase segregation was detected in the tested range of incorporated nano-Al2O3 and sintering temperatures.

Abstract: Porous ZrO2 single crystals were prepared through a sol-gel-hydrothermal method and characterized by XRD, HR-TEM, SEM and FT-IR. The results show that the dried sol gel was converted into monoclinic zirconia crystals after calcined above 550 °C. The zirconia single crystal has a porous structure with the crystal sizes of 20-70 nm. The origin of the pores was the gaseous hydrolysates of the superstoichiometric urotropine. The gel structure and the hydrothermal treatment are the required conditions resulting in the pores in crystals. After sintered at 1400 °C, the disc of the obtained ZrO2 crystals was dense. However, Y2O3 should be added to avoid fracture due to phase change if the disc was used as heat insulating layer.

Abstract: The zirconia refractories were prepared using partially stabilized zirconia grain and monoclinic zirconia powder as the matrix, partially stabilized zirconia particles as the aggregate, and phenolic resin as the binder, and four sizes of monoclinic zirconia powder (D50=1 μm, 3 μm, 6 μm, 10 μm) were used as additives. Besides, an improved specimen was prepared using a specific monoclinic zirconia powder as additive. Properties of specimens with different sizes of m-ZrO2 powders were researched, including apparent porosity, bulk density, cold modulus of rupture, pore size distribution. Moreover, phase composition and microstructure were analyzed. The results show that, particle size of monoclinic zirconia powders greatly affect the sintering of materials. The specimens with finer m-ZrO2 powder have lower porosity, higher bulk density and cold modulus of rupture, and the grain boundaries of zirconia particles were fuzzy, showing that the matrix of the specimens were almost sintered completely. While in specimens using coarser m-ZrO2 powder, the grain boundaries of zirconia particles were clear, showing that the matrix of the specimens were not sintered completely.. Though finer monoclinic zirconia powder promoted the sintering of materials in the test, it had negative impact on the microporus structure, for large pores were observed in the specimen with fine m-ZrO2 powder. Finally, the improved specimen with promoted sintering and optimized microstructure as well as phase composition was obtained by using specific monoclinic zirconia powder as additive.

Abstract: Nano-sized 8mol% MgO-PSZ powder was prepared via coprecipitation, Afterwards, the prepared powders were characterized by XRD and SEM technologies. The results clearly demonstrate that the calcined temperature can be feasible for the MgO-ZrO2 composite, crystal structure and particle size.